The best and most effective answer you have gotten (IMHO) is ...
PRACTICE.
Get the coach to an empty parking lot and keep at it. I had driven big things all my life, but it took DW (now the primary driver - her choice) a full day to be comfortable parking near other things.
Again.
Practice
If you want a set of signals so the SO can help direct, that is good, but you have to agree on them BEFORE you start and the outside director has to understand the s/he has to be where s/he can be seen easily either in the driver's side mirror or window. (Don't try to use the passside mirror, it just doesn't work.)
Matt